1. The Field of the Invention
The present invention relates to upflow bioreactors for decomposing organic materials. More particularly, the present invention relates to an upflow bioreactor having an auger and drive assembly.
2. The Related Technology
A bioreactor is a device that uses bacteria to promote the decomposition or “digestion” of organic waste material into simple organics and gaseous biogas products. Biogas is typically a mixture of methane, carbon dioxide, hydrogen sulfide, and other volatile organic compounds. If produced in sufficient quantities, the methane gas can be used as a fuel.
Anaerobic digestion in open storage vessels has historically been utilized in waste water management, especially in livestock production, to reduce or convert complex organic matter to a smaller volume. This method has proven to be economical by reducing the volume of waste handled and by volatilizing some metabolites into the atmosphere. One disadvantage of open storage vessels includes the inability to keep the anaerobic digestion process in balance, resulting in the release of malodorous gases and inefficient, incomplete conversion of digested organic matter into biogas. In addition, the slow rate of digestion and the poor quality of methane gas yielded makes the economic recovery of methane gas generally unfeasible in open storage vessels.
Many attempts have been made to decompose organic waste using closed vessels. One type of closed vessel reactor that has shown high decomposition rates is the upflow anaerobic sludge blanket reactor. In the reactor, waste material is introduced into the bottom of the reactor and forced up through the vessel where it passes through a blanket of bacteria, which decomposes the organic material and produces biogas that can be collected and used as a fuel.
To achieve high decomposition rates in an upflow bioreactor, the bacterial culture should be well established. One important advantage of an upflow bioreactor is that it can be operated continuously. Thus, once the bacterial culture is established, the high rate of digestion can be maintained for an extended period of time (e.g. months or even years).
Recently an upflow reactor has been developed that induces formation of the bacterial culture on startup and maintains a thicker or more enriched bacterial culture during operation. These benefits are achieved by placing a septum near the top of the fluid level of the reactor. The septum causes suspended solids to settle out of the fluid nearing the top of the reactor. These solids settle back into the sludge blanket where digestion continues. The solids that are retained by the septum often include bacteria. By retaining these solids in the digester, the septum maintains a better bacterial culture and facilitates more complete digestion.
To allow the effluent to exit the digester, the septum has an aperture. Since an aperture in an upflow bioreactor can plug, an auger is placed in the aperture. The auger hangs from the top of the digester and slowly turns to keep the aperture clear of solids.
Upflow digesters that include a septum and an auger can be difficult to construct because of the need to accurately line up the auger within the aperture of the septum. In addition, the top of the digester needs to be sealed to form a chamber for collecting biogas.